Abstract Spawning ponds of Florida largemouth bass Micropterus salmoides floridanus were fertilized with liquid inorganic fertilizers and either cottonseed meal (CSM) or no cottonseed meal (NOCSM) to evaluate the effects of organic fertilization on largemouth bass fry production, plankton densities, and water quality. Each treatment consisted of eight replicate ponds. All ponds of both treatments were subjected to the same inorganic fertilization regimen. Nitrogen and phosphorus levels were similar between treatments. Morning and afternoon dissolved oxygen levels were significantly lower in CSM ponds than in NOCSM ponds throughout much of the culture period. Levels of total CO2 were significantly higher in CSM ponds than NOCSM ponds. Higher total CO2 concentrations apparently contributed to significantly lower pH levels in CSM than in NOCSM ponds. Phytoplankton biomass preceding crustacean zooplankton density peaks was significantly higher in CSM than in NOCSM ponds. Cladoceran and rotifer densities were ...